IGN outputs for led

Trickster
Posts: 63
Joined: Mon Nov 28, 2016 6:09 pm

IGN outputs for led

Post by Trickster »

Hi
I am running low on outputs so was going to use my 2 spare ignition outputs of my s6 for leds as shift lights.
Pat says no more than 40ma draw on these outputs
If I use white leds with 470 ohm resistors they should pull 6ma each on the 5v output.
Does that sound OK?
Also is there any short circuit protection or anything on these outputs? If not I'll only use one so I have a spare incase one of my actual ignition outputs goes down
Graeme
MR2 Turbo 5sgte 750hp 527ft/lb Syvecs S6
stevieturbo
Posts: 983
Joined: Sun Dec 07, 2008 2:04 pm

Re: IGN outputs for led

Post by stevieturbo »

You can get 12v LED's for cars etc...No need to add complication with 5v.

Pretty sure it's been covered before the outputs are fine for that type of thing

eg, these list some spec, 20mA at 12v. I'm sure most would be similar ?

https://www.ebay.co.uk/itm/12V-Pre-Wire ... Sw9PFbzdDx
Trickster
Posts: 63
Joined: Mon Nov 28, 2016 6:09 pm

Re: IGN outputs for led

Post by Trickster »

The ignition outputs are 5v outputs unless you open the ecu up and change the jumper which I don't want to do.

And I already have leds and resistors.

I just want to be on the safe side so I don't fry those outputs

Graeme
MR2 Turbo 5sgte 750hp 527ft/lb Syvecs S6
stevieturbo
Posts: 983
Joined: Sun Dec 07, 2008 2:04 pm

Re: IGN outputs for led

Post by stevieturbo »

off may be 0v or 5v, but when the output is on...it's grounded, so 12v devices would be fine, same as a relay would be fine.

Although if the off state is at 5v for example....then I guess there may be a chance of a small glow from the led ?

Either or, if there are 5v LED's no issue as long as they do not draw too much current from wherever you get your 5v supply from.
Trickster
Posts: 63
Joined: Mon Nov 28, 2016 6:09 pm

Re: IGN outputs for led

Post by Trickster »

Ohhh that's making more sense, I actually thought it was normally 0v and put out +5 when it switched as it is a TTL output so I assumed it generated a square wave switching between 0v and 5v (I'm no electronics expert haha)

So I assumed you would take the output to the led and ground the other side.

You are saying wire it as any other fuel/pwm output?

Graeme
MR2 Turbo 5sgte 750hp 527ft/lb Syvecs S6
TimH
JT Innovations
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Re: IGN outputs for led

Post by TimH »

stevieturbo wrote: Sat Apr 18, 2020 10:30 am off may be 0v or 5v, but when the output is on...it's grounded, so 12v devices would be fine, same as a relay would be fine.
S6 ignition outputs are 5V TTL and switch 0V->5V, not grounding unless you go inside the ECU and change things.

The proposed solution will work fine.

Not sure about protection - I would hope there is, as that would be good design practice. I have not heard of an S6 ignition output failing - they are used for 6 cylinder engines so there's no spare there either. I would just wire the LEDs in and be done with it!

As an aside, is there a CEL output assigned? That is often re-purposed as a shiftlight (default is often a knock warning light).
TimH
JT Innovations
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Joined: Wed Sep 01, 2010 2:51 pm

Re: IGN outputs for led

Post by TimH »

S6 GP that is. S6+ has more easily accessible "solder bridges" to change things.
Trickster
Posts: 63
Joined: Mon Nov 28, 2016 6:09 pm

Re: IGN outputs for led

Post by Trickster »

I already have a shift light I just want 2 stages, and I have a knock warning light also (just getting everything out of my ecu haha)

I did try using the ignition output to trigger my solid state relay for my fuel pump as that is supposed to trigger at 3.5v but it didn't work, I'll connect some leds up and do some tests first.

I would prefer to run my solid state relay off the ignition outputs so I don't have to worry about current draw of leds meaning I could use a small array for viability.

Graeme
MR2 Turbo 5sgte 750hp 527ft/lb Syvecs S6
TimH
JT Innovations
Posts: 662
Joined: Wed Sep 01, 2010 2:51 pm

Re: IGN outputs for led

Post by TimH »

Sorry for drip feed as I think of things!

White LEDs have a forward voltage of 3-3.5V - when I last used a TTL output (to drive a solid state relay) I found it was actually only about 3.5V. - and didn't drive the SSR properly as you found. TTL output voltage spec means that is "in range" - but you may struggles to actually drive an LED, especially a white one, directly anyway, and for it to be usefully bright.
stevieturbo
Posts: 983
Joined: Sun Dec 07, 2008 2:04 pm

Re: IGN outputs for led

Post by stevieturbo »

TimH wrote: Sat Apr 18, 2020 10:48 am
Not sure about protection - I would hope there is, as that would be good design practice.
I busted a fuel output on an S6...so no protection there.
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